Electrical pulse time modulation circuit



D. D. GRIEG ETAL ELECTRICAL PULSE TIME MODULATION CIRCUIT Dec. 13, 1949 2 Sheets-Sheet 1 Filed March 2, 1946 TRANS/410751? INVENTORj` TTDRNFY Patented Dec. 13, 1949 ELECTRICAL PULSE TIME MODULATION CIRCU Donald D. Grieg and Arnold M. Levine, Forest Hills, and Sidney Moskowitz, New York, N. Y., assignors to Federal Telecommunication Laboratories, Inc., New York, N. Y., a corporation of Delaware Application March 2, 1946, Serial No. 651,650

4 Claims.

This invention relates to a pulse time modulation system. More particularly, it deals with a multichannel system for time modulating interleaved trains of pulses with respect to audio or other frequencies' of intelligence.

An object of this invention is to time modulate pulses in a simple, novel and effective manner.

It is another object to provide a novel and effective multichannel pulse time modulation system.

It is another object to reduce cross-talk between the signals in different channels of a multichannel modulation system by limiting the signal input before it is modulated.

It is another object to provide a novel circuit for mixing the pulses of several channels on a single multichannel electromagnetic wave.

It is another object to provide a novel circuit for shaping the pulses in a pulse modulation system after the pulses have been modulated.

It is another object to provide a common circuit for mixing and shaping the modulated pulses of separate signal channels onto one multichannel pulse Wave.

It is another object to provide a novel method of producing a steady marker or synchronizing pulse for a multichannel pulse time modulation system which marker pulse will not drift in time with respect to its regular repetition rate.

Other objects and features of this invention will appear from time to time in the description which follows:

Generally speaking, the pulse time modulation system of this invention comprises the following essential elements: (l) a base wave generator for producing a train of regularly recurring undulations, each of which undulations has a sloping, leading or trailing edge preferably of substantially constant slope; (2) a signal input circuit which may contain a limiter to limit the amplitude of the input signal; (3) a double clipper or gate modulator circuit in which the undulations on the base waveiare clipped along theirl sloping 'edges at different amplitudes corresponding to 'the output from the signal input circuit; and (4) a pulse Shaper circuit for producing time modulated pulses corresponding to the sloping edges 'of the portionsclipped by the gate modulator from the base wave. If this system is employed for producing a multichannel pulse wave wherein a plurality of trains of pulses corresponding to different signal channels are interleaved on a separate base waves for each signal channel, means for producing a marker or synchronizing pulse on the multichannel pulse wave so that the diierent channels may be separated therefrom at the receiver, and suitable means for mixing or interleaving the separate trains of pulses corresponding to each signal channel, as well as the train of marker pulses. This latter mixing means may be combined with the Shaper element (4) for mixing the trains of time modulated pulses, and/or a separate mixer means may be provided for mixing the marker pulses with the time modulated pulses.

These and other features and objects of this invention will become more apparent upon consideration ofthe following detailed description of an embodiment of the invention to be read in connection with the accompanying drawings in which:

Fig. 1 is a schematic block Wiring diagram of a preferred embodiment of the multichannel time modulation system of this invention; and

Fig. 2 is a graph of wave forms useful in explaining the operation of the system shown in Fig. 1.

Referring to the drawings, I is a base wave generator and a separator circuit from which may be withdrawn one or more base Waves 2, 3, 4 and 5 (see Fig. 2), each of which contains a regular recurring undulation having a sloping edge, the leading edge, for example. In' a multichannel system it is important that these waves be of the same frequency but be out of phase With respect to each other as shown in Fig. 2. Each one of the separate waves 2, 3, 4 and '5 is shown to be reserved for a different signal channel (as indicated in Fig. 2), namely, wave 2 is for the marker or synchronizing channel M, and Waves 3, 4, 5, etc., are for signal channels a, b, c, d. e,

. n, respectively.

The circuit I Amay comprise a plurality of separate saw-tooth wave generators or Shapers or each Shaper may be connected to a single Wave generator from which each of the separate channel waves are delayed different amounts so as to be out of phase with each other. This delay may be accomplished by a plurality of taps along a suitable del-ay line or by an electronic distributor means such as a Cyclophon described in the copending application of D. D. Grieg et al., Ser. No. 651,651, filed March 2, 1946. Although triangular shaped pulses are shown onthe waves 2, 3, 4, 5, any shaped pulse which has a leading or trailing sloping edge, the slope of which is substantially constant on the recurring pulses, could 8, in the double clipper and modulator circuit- 9. The signal to be modulated is also applied to the grid 1 through the audio--input circuitl IIJ coupled to line 6 at the point II.

through line I2 and is preferably amplified in an amplifier circuit I3 before being-passed onto thel point II.

The amount of modulation producedincircuit 9 may be limited by limiting the amplitude of the signal a before it is introduced into the circuit 9. This is particularly advantageous in the case of @multichannel pulse timer... modulation system whereinthe higher amplitude signals often produce` cross-talk -betweenadjacent channels along the multichannel-gpulse,` waves.; Thus, by limiting theamplitude ofthe. input signal and thereby the amountAofftimevv modulationY of-'each pulse. the amount of such` cross-,talkis 4materially reduced. Theflclrclvlitafor limiting this amplitude may comprise a coupling condenser Ilfin the line I5 from the. gampliijerv I 3 and a, pairof i opposed rectiers I6 andi? in parallel lwith-eacl'i4 other, one of which is biased-:negatively andrtheothcr of which is biased vpositively to the respective maximum amplitudes desired for the signal; to be applied to the` gridfl, These.reotiiie rs ,,WandA l'I may comprise. diodes-crystal r.eci{rulers-,1or.y any .other tyre of valve which will permittheflowyof current in one direction; only; Since these` two rectiiiers only pass the current in opposite directions, both thevpositive andthe negative maximum amplitude ofthe signal in line-.I whichis passed on through resistorsIS to point I Igwill-befdetermined by the highestA negative .and positivebiasesy applied to rectiiiers ISf and-V I l,.- respectiyely- For example, if these rectifiers were biased to +10 and 10 volts, and the` input..signal in; line I5 had an amplitude of v+;-and ,-lgvolts, Vonly. +10 and -10 volts vwill beapplied tothe pointI I, the remaining portions, of thesignll passing through inlineIE were.less.than rlovvolts, say i8 volts, theentire signal woulclbe applied 'to-point I I and thence. to .grid .1, y Without anydecrease in amplitude since neither. rectifier.. I6rnor I1 would becomeccnductive becauseits applied bias would not be overcome.. This. limiter .p comprising the two .oppositelybiased rectiers IB. and Il in the signal inputcircuit I0, thereby limits the amplitude at which; thedoubleclipperor gate modulator 8 will clip sections from thelundulations on This gate is movedup--and,downaccording to the signal applied from thecircuit I0-to the grid 1. The` detailswof the operation, of. such` a double triodegate modulator arefully described inthe @grandine applicati@ oi.E.I-abi,r.1..et al., `Serial N05 '155;898,v led August 24\.. .1Qi42,. now U- S- Signal channel a, which may be a code, audigyvfacsirnile, video, or the like, signal is introducedv to the circuitl I0 pulses 33 on wave 34 (in Fig. 2).

Patent No. 2,434,936. Thus, the output from plate 22 of gate modulator tube 8 in line 23 is similar to that shown on wave 24 in Fig. 2. The pulses on this wave 24, for example, correspond to the shaded clipsection 25 from undulation 26 on wave Svafter it has been'amplied to produce the pulse 21 on Wave 24. The important part of this pulse 2 is the time position of its leading edge 28 which corresponds respectively to the portion along the sloping leading edge of the pulse 25 at which the gate ZI clips the pulse 26. The signals applied at point Il from the circuit I0, therefore, moves the gate 2| up and down Within the limits I9 and 23 according to the amplitudeof the signal a introduced into circuit I0. The greater this amplitude the higher the gate 2l is along the edge of the pulses 26 and the more time delay there will be for the leading edge of-the pulse 2l on the wave 2li. Accordingly, the amplitude signal from the circuit i@ thereby is converted into a time, modulated signal by the double clipper or gate modulator circuit 5 to pro-` duce the pulse wave 24. may be passed through a resistor 29, inserted in the circuit for isolation purposes in the ca se of a multi-channel system, before it is introduced into the shaper circuit 3?, which in a mu1tichannel system also .may be a mixer,

The shaper circuit 30 comprises aninductance 3| and a rectier 32 (which may be similar to the rectifier i5 or il) coupled inl parallel. The function of the inductance 3| is to diierentiate the wide pulses 21 on wave 24 to produce the positive This inductance 3I in the absence of the rectier 32 would also differentiate the trailing edge of pulse 27 to prof duce the negative pulse 35, shown dotted on Wave 361.k However, the rectiiier-32 is biased to a B+ voltage supply so that all negative undulations Will be shunted out through the rectifier 32 thereby producing a .waveof vonly positive pulses corresponding in timeA to the leading edges of the pulsesI on Wave 22.* This positive pulse wave may then be withdrawn from the circuit 35i through line 36 to any suitable .utilization circuit, such as in avradio transmitter. In the case ofi-a multichannel system, line 36 may becoupled to a mixer 31 for mixing it with a marker pulse before it is passed on through line 38 to avtrans-mitter. If the trailing edge ,rather thanthe leading edge of the base wave pulses are to be used, the input to Shaper circuit 30 must be pulses of opposite polarity to those shown on the rectifier. 32 must be reversedto pass only negative pulses tothe commonline circuit.

If it is desired, a marker pulse or synchronizing pulse may be produced from Aa separate channel base wavel and stabilized in acircuit similar to that employed for channel a described above. Referring to the ',drawings, then/'ave Zmay .be Withdrawn wave. generatori through line 39 into a `double clipper `circuit @similar to 9 except that anxed bias is applied tothe grid? through a .suitable resistance coupled between `the grid'l in.-

putcircuit and the ground. Otherwise, the circuiti) would be identical to that used incircuit lland the xed gate Would-clipthe undulations on wave V2 between the clipping levels 42. Circuit i) also may be. followed. by ashapercircuit 4I which may be identical with the circuit 30 de- -scribed above for shaping the pulses. The output from the shaper 4I. through line 43 would therefore be, similar tothe wave lllvshownVV in Fig.p2 except only the first of the .parir of pulses The wave 2d in line 23- would be present. The synchronizing or marker pulse wave then may be passed into a suitable marker pulse generator circuit 45 which may comprise the delay line for producing the double -pulses as shown on wave 44, or may produce a wider pulse or any other shaped pulse which may be distinguished easily from the time modulated pulses on wave S4. A circuit for producing the double or pair of marker pulses shown on wave 44 is described in the copending case of D. D. Grieg, Serial No. 625,650, led October 30, 1945, now U. S. Patent No. 2,485,591, issued October 25, 1949. Thus, from wave 44 withdrawn from generator 45 through line 46, may be passed into a suitable mixer 31, which may comprise a pair or more of triodes or other vacuum tubes the plates of which may be coupled together so that the waves 44 and 34 will .be combined to a multichannel wave, such as wave 41 shown in Fig. 2 if only a marker pulse M and signal channel a pulses were shown thereon.

Similarly, other signal channels b, c, d n may be modulated in circuits similar to circuits 9 and l@ by passing the wave 4 through line 4B into a suitable double clipper modulator 49 (similar to circuit 9) controlled by output of the limiter circuit 50 (similar to circuit l0) coupled through point El and into which signal b is applied through line 52. From the double clipper modulator i9 for signal b may be withdrawn Wave 53 through line 54 which may be then passed to a shaper similar to shaper 39 or to the same shaper 39 coupled to the modulation circuit for signal channel a as is shown. Since the plates of all the modulator tubes 8 are connected together and to the circuit 30 and since the pulses produced in the separate modulator circuits are out of phase with each other, there will be no feedback from one modulator .circuit into another. Therefore the outputs from a plurality of modulator circuits can be connected to the same shaper circuit 30 as shown.

Similary, other channel demodulator circuits may be coupled to lines 56 from the base wave generator and separator circuit I to other channel signal input or limiter circuits and other channel double clipper modulator circuits to produce waves 51, etc., and from it waves 58, etc., which are then passed through line 59 coupled to the input of the circuit 30. Thus, from circuit 30 in line 36 is withdrawn a wave similar to 41 shown in Fig. 2 without the marker pulses M. These marker pulses may be combined or interleaved With the time modulated pulses in the mixer 31 to produce the wave 41 as shown in Fig. 2. This multichannel pulse wave 41 may be passed through line 38 to any suitable utilization circuits such as a transmitter for transmission by radio or over a cable as desired.

While the above describes one specific embodiment by way of illustration, many variations in the details thereof may be had without departing from the scope of this invention. The specio description shown here is given by way of example, and is not intended as a limitation of our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

1. A pulse time signal modulation system comprising: a signal source, a signal input circuit to limit the amplitude of the signal from said source; means for producing a train of pulses, each of said pulses having a sloping edge; a double clipper means for clipping the pulses at two levels along their sloping edges at various amplitudes determined by the output from said signal input circuit to produce variable width pulses and means for differentiating said variable width pulses to produce time modulated pulses corresponding to the sloping edges of said portions. 2. The system of claim 1, wherein the slope of the edges of all of said pulses is substantially the same.

3. A pulse time signal modulation system comprising; a signal source, a signal input `circuit including two `biased rectifiers to limit the :peak amplitudes of the signal from said source to a given maximum level; means for producing a train of pulses, each of said pulses having a sloping edge; a double clipper means for clipping the pulses of said train at two levels along their sloping edges at various amplitudes determined .by the output from said limited signal input circuit to produce variable width pulses having a maximum variation determined by said maximum level; and means for di'erentiating said variable width pulses to produce time modulated pulses from the sloping edges of said portions.

4. The system of claim 3, wherein said rectiers are crystal rectiiiers.

DONALD D. GRIEG. ARNOLD M. LEVINE. SIDNEY MOSKOWITZ.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,391,776 Fredendall Dec. 25, 1945 2,401,384 Young, Jr. June 4, 1946 2,403,210 Butement et al July 2, 1946 2,416,329 Labln et al. Feb. 25, 1947 2,418,116 Grieg Apr. 1, 1947 2,419,535 Chatterjea Apr. 29, 1947 

